In a conventional musical sound generating system used for electronic musical instruments such as an electronic piano, when a key is pressed, a musical sound signal is produced based on the pre-stored waveform data corresponding to the pressed key which is then amplified and converted to a musical sound by a loudspeaker. At the same time, the amplitude of the higher frequencies and the tone of the musical sound to be generated are changed in accordance with the key pressing speed. Specifically, as the key pressing speed is increased, a musical sound with a higher amplitude of high-frequency components, i.e. a musical sound in brighter tone, is generated.
A typical example of an electronic musical instrument of this type is one in which a musical sound signal, based on waveform data, is passed through a low pass filter, the cut-off frequency of which is controlled according to the key press intensity, thereby high-frequency components of the musical sound signal are attenuated. In this electronic musical instrument, when a key is pressed with a strong touch, a higher cut-off frequency is set such that the output is performed with an increased amplitude of high-frequency components, while a lower cut-off frequency is set such that the output is performed with a decreased amplitude of high-frequency components when a key is pressed with a weak touch.
Another example is an electronic musical instrument in which a plurality of musical sound signals having different distributions of the amplitude of frequency components and a plurality of envelope waveforms corresponding to the musical sound signals respectively, are prepared for generating a musical sound by the press of one key. When a key is pressed, a plurality of signals are produced by multiplying each musical sound signal and the corresponding envelope waveform, and by combining the signals with each other a musical sound in a desired tone is generated.
The aforementioned envelope waveform represents variation of the amplitude of a musical sound generated by a musical sound signal with time. In this electronic musical instrument, the tone of the musical sound to be generated can be changed by controlling the amplitude of the plurality of envelope waveforms according to the key press intensity. Specifically, in an electronic musical instrument of this type, when a key is pressed with a strong touch, a musical sound in a bright tone is generated by increasing the amplitude of the envelope waveform corresponding to the musical sound signal having a frequency distribution with a high amplitude of high-frequency components (or by decreasing the amplitude of the envelope waveform corresponding to the musical sound signal having a frequency distribution with a small amplitude of high-frequency components). When a key is pressed with a weak touch, oppositely, a musical sound in a dull tone is generated by decreasing the amplitude of the envelope waveform corresponding to the musical sound signal having a frequency distribution with a high amplitude of high-frequency components (or by increasing the amplitude of the envelope waveform corresponding to the musical sound signal having a frequency distribution with a small amplitude of high-frequency components).
Generally, the volume of musical sounds generated from a loudspeaker is controlled in accordance with the amplification factor of an amplifier, which a user can set. When a user sets the amplification factor low, the user unconsciously tends to press the keys with a strong touch (i.e., rapidly) because the output volume of the loudspeaker is small. As a result, the generated musical sounds include a larger amplitude of high-frequency components, which results in a bright tone thereof. When the user sets the amplification factor high, the user unconsciously tends to press the keys with a weak touch (i.e. slowly), which results in the generated musical sounds with a small amplitude of high-frequency components and thus in a dull tone. Thus, there is a problem that the setting of the amplification factor produces a psychological effect on the user such that the tone of the generated musical sound is different from that which the user desires.